北半球干旱区降水转化和再循环特征及其在全球变暖背景下的变化

发布时间：2018-03-10 15:46

本文选题：降水　切入点：蒸发　出处：《兰州大学》2017年博士论文　论文类型：学位论文

【摘要】：水分循环是研究气候变化中的一个基本内容,也是降水发生的基本条件之一。水分循环过程既影响着陆气之间水分交换的变化,也影响着大气的能量收支,既对气候变化响应,也对气候产生影响。干旱区降水稀少,水汽来源匮乏,水分循环中的局地水分循环在降水中占有多大比例是一个基本科学问题;同时,蒸发是水分循环中的重要环节,蒸发量的估算是定量评估水分循环的关键,和同纬度其他气候区相比,干旱区平均气温偏高,土壤湿度偏低,使得蒸发的估算具有较大不确定性,如何客观准确的估算蒸发是一个值得探索的科学问题。本文通过使用NCEP、EAR-Interim、GLDAS等多种再分析及模式输出资料的综合计算、诊断分析,在比较不同蒸发估算方法的基础上,探索、发展了一个相对合理、且客观定量的蒸发计算方法;分析了全球温度显著升高的近30年(1981-2010),北半球典型干旱区水分循环中降水转化及再循环的时空特征,并利用CMIP5结果对21世纪不同时期(初期:2017—2036,中期:2047—2066,后期:2077—2096)、典型干旱区的水分循环时空变化进行了预估,并探讨了温度升高情况下水分循环变化的可能机制。首先,本文把北半球干旱区分为中蒙、西亚、北非和北美干旱区四个区域,利用Penman—Monteith蒸发及Brubaker再循环模型,计算了北半球典型干旱区的年平均降水再循环率。结果显示,中蒙、西亚、北非和北美干旱区的年降水再循环率分别为5%、12%、18%和8%。降水量最少的西亚、北非干旱区的降水再循环率大于中蒙、北美干旱区,表明在干旱地区,局地水汽贡献对总降水的贡献更大。在过去的30余年来,随着全球气温的上升,西亚干旱区的降水再循环率呈现出增加趋势,而降水呈现出减少趋势,尤其自1981年以来,该地区降水减少,同时降水再循环率以0.43%10a-1的速率增加,表明在全球变暖背景下,由于水汽输送在该地区为净输出,因此降水再循环率在降水减少过程中起着补偿作用;在北美和北非干旱区的再循环率为减少趋势(-0.45%10a-1和-0.26%10a-1)。在北美干旱区,Penman蒸发增加(0.07 mm day-1 10a-1)、可降水量增加(0.12 kg m-2 10a-1),但总降水减少(-0.02 mm day-1 10a-1),表明通过蒸发从下垫面进入大气的水汽增多,但是并未转化为实际降水。而在北非干旱区,降水为增加趋势(0.06 mm day-1 10a-1),对应降水再循环率减小,外部水汽输送增加。这表明外部水汽输送增加使得北非干旱区局地贡献水汽在总降水中的比率降低,降水增加。总体而言,外部水汽输送仍然是降水的主要来源,降水再循环在降水出现减少趋势时起到补偿的作用。蒸发的估算对于水分循环起着决定性的作用。但是,实际的蒸发很难估算。为了减小参考蒸发和实际蒸发之间的差别,本文通过对比Penman蒸发以及利用土壤湿度修正后的改进蒸发,应用动力降水再循环模型DRM,计算亚非干旱区降水再循环率,分析结果表明受限于有限的土壤水分,干旱区蒸发量(0.3—0.8mm day-1)小于参考蒸发量(4.4—11.0 mm day-1)。通过比较降水再循环率与ET-P发现,中蒙、北非干旱区降水再循环率降低,同时外部水汽输送在总水汽中比例升高,对应ET-P减小,陆面水汽支出减少,西亚干旱区水汽为净输出、降水再循环率增加,局地水汽贡献在总水汽中增加,对应ET-P增加。这表明降水再循环过程对于在亚非干旱区的干旱有负反馈机制:降水再循环率降低,对应更多外部水汽输送进入干旱区,总降水中局地水汽贡献比例降低,外部水汽供应与内部水分循环相配合,表现为干旱区ET-P减小,陆面水汽支出减少,干旱程度减弱。与此相反,当降水再循环率增加时,外部水汽输送减弱,局地水汽作为补偿更多参与降水过程,ET-P增加,陆面水汽输出增加。水汽在大气中存在的时间也影响着降水的再循环率。本文选取中蒙干旱区3次典型个例,分别代表对流型及平流型降水过程,利用WRF和FLEXPART模式对3次个例进行了模拟分析。结果表明:中蒙干旱区降水及再循环过程中,正午局地蒸发大于降水,陆面水汽通过蒸发进入大气,局地水汽贡献达到最大(0.1mm),再循环过程开始增强,在傍晚达到最大(10%),降水再循环对降水有增强作用,降水转化率同时达到最大(7%),降水、蒸发也同时达到最大。此后局地水汽贡献量逐渐减小,在凌晨至清晨蒸发达到全天最低,局地水汽贡献为负(ET-P-0.2 mm)。而这一特征在平流型降水过程中更为明显。此外,通过分析选取个例中降水等变量的日变化特征,结果表明中蒙干旱区降水、蒸发、降水转化及降水再循环率均存在准10天的变化周期,这与气候平均的结果相近。并且在日尺度上降水再循环对于降水变化存在负的反馈机制:当降水减小后蒸发增加,更多水汽由地面进入通过蒸发进入大气,参与降水再循环,补偿降水减少。而在空间分布上,中蒙干旱区降水再循环率分布不均匀,在湖泊,径流及地面湿度较大地区,由于蒸发较强,降水再循环率偏强。在降水过程中,外部水汽贡献主要以纬向水汽输送为主,占总水汽量40%左右。而经向输送水汽则占7%~20%,且经向水汽输送偏强时,降水量较大,反之亦然。全球变暖对水分循环有着重要的影响。本文分析了未来不同排放情景下水分循环的变化特征。结果表明,大气的可降水量在未来不同升温阶段均出现了不同程度的增长趋势和分布,这是由气温升高增加了大气的持水能力所致。并且ET-P存在干旱区增加、湿润区减小的趋势,表现出干旱区越干,湿润区越湿的变化趋势,同时干旱区降水转化率及降水再循环率为减小趋势,表明随着全球温度的上升,干旱区局地水分循环减弱。在未来的21世纪的不同时期,全球陆地平均降水转化率和再循环率均表现为减弱趋势,分别减少1.5%和0.7%,RCP8.5情景下减小更为明显,负距平为-2.7%和-0.9%。其中在典型干旱区,可降水量将随温度升高而增加,增加趋势最大可达1.85 mm day-1 10a-1。虽然大气的水汽含量增加显著,但干旱区水汽的转换率降低,表明全球温度升高使得大气的持水能力增加。而干旱区总体表现为水汽净输出,降水再循环率的减少表明,局地蒸散水汽由于平流作用输出,并未参与局地降水再循环。总可降水量中,来自外部平流水汽的输送增强且加快,这表示全球变暖,大气的水分循环加快。而ET-P无显著的变化趋势,表明大尺度水分循环加速并不会使得中蒙干旱区发生显著的干湿变化。
[Abstract]:The water cycle is one of the basic contents of climate change, but also one of the basic conditions of the occurrence of precipitation change. Water cycle not only affects the gas exchange between the water landing, also affects the energy balance of the atmosphere, as well as response to climate change, but also have an effect on the climate. In arid area of precipitation, water vapor sources, local water circulating water circulation in occupy much of the precipitation which is a basic scientific problem; at the same time, evaporation is an important part of the hydrologic cycle, estimated evaporation is a quantitative assessment of key water cycle, compared with the same latitude climate region, arid area average high temperatures, low soil moisture, the evaporation the estimation with uncertainty, how to objectively and accurately estimate the evaporation is worth exploring scientific problems. In this paper, through the use of NCEP, EAR-Interim, GLDAS and other analysis and mode Comprehensive calculation, output data diagnostic analysis, exploration based on comparison of different estimation methods of evaporation, and the development of a relatively reasonable, objective and quantitative calculation of evaporation method; analysis of the global temperature increased significantly over the past 30 years (1981-2010), temporal and spatial characteristics of precipitation conversion and recycling water in typical arid area in north loop hemisphere, and the use of CMIP5 results of different periods in twenty-first Century (early: 2017 - 2036, 2047 - 2066, the middle late: 2077 - 2096), water cycle temporal changes in typical arid area were estimated, and explore the possible mechanism of temperature change of water cycle conditions. First, the northern hemisphere drought Mongolia is divided into four regions, West Asia, North Africa and North America arid area, using Penman - Monteith and Brubaker evaporation recycling model, the average annual precipitation recycling in typical arid region of the northern hemisphere was calculated. The results show that in Mongolia, West Asia, North Africa and North America arid area of annual precipitation recycling rates were 5%, 12%, 18% and 8%. precipitation in arid area of North West Asia, precipitation recycling rate is greater than the Mongolia, arid region of North America, shows that in arid areas, local water vapor contribution to the total precipitation is greater in the past 30 years. Come, as global temperatures rise, the rate of precipitation recycling in arid area of West Asia showed increasing trend, and the precipitation showed a decreasing trend, especially since 1981, the rainfall decreased, while precipitation recycling rate increased at the rate of 0.43%10a-1 showed that, under the background of global warming, due to water vapor transport in the region is a net output. The precipitation recycling rate in precipitation reduction plays a role in the process of compensation; in order to reduce the trend in the arid region of North America and North Africa recirculation rate (-0.45%10a-1 and -0.26%10a-1). In the arid region of North America, Penman (0.07 increase in evaporation Mm day-1, 10a-1) can be increased precipitation (0.12 kg m-2 10a-1), but the total precipitation reduced (-0.02 mm day-1 10a-1), that enters from the surface and atmosphere through evaporation of water vapor increased, but did not translate into actual precipitation. In the arid region of North Africa, an increasing trend in precipitation (0.06 mm day-1 10a-1). The corresponding precipitation recycling rate decreases and the increase of transport water vapor. This suggests that external external water vapor increases the local arid region of North Africa with water vapor ratio in total precipitation decreased in precipitation increased. Overall, the external water vapor transport is still the major source of precipitation, precipitation recycling in precipitation decrease when the role of compensation evaporation. The estimation plays a decisive role in the water cycle. However, it is difficult to estimate the actual evaporation. In order to decrease between the reference evaporation and actual evaporation difference, through the comparison of Penman and the use of soil evaporation The improved soil moisture evaporation after modification, application of dynamic precipitation recycling model DRM, the calculation of precipitation recycling ratio arid region in Asia and Africa. The analysis results show that due to the limited soil water evaporation, arid area (0.3 0.8mm day-1) less than the reference evapotranspiration (4.4 - 11 mm day-1). By comparing the precipitation recycling ratio and ET-P found Mongolia, arid region of North Africa precipitation recycling rate decreased, while the external water vapor increased proportion in the total water vapor, the corresponding ET-P decreases, the land surface moisture spending, west arid region water vapor net output, precipitation recycling ratio increased, the local moisture contribution in the total water vapor increases, the corresponding ET-P increased. This suggests that the precipitation recycling process negative feedback mechanism in arid region of Africa and Asia: drought precipitation recycling rate, corresponding to more external water vapor into the arid area, the proportion of total precipitation reduced water vapor with local, external water vapor The supply is matched with the internal water circulation, for arid area ET-P land surface water vapor decreases, spending, the degree of drought weakened. On the contrary, when the precipitation recycling rate is increased, weakening external water vapor transport, local water vapor as compensation for more participation in the precipitation process, the increase of ET-P, the land surface vapor output increased. In the presence of water vapor in the atmosphere the time also affects the precipitation recirculation rate. This paper chooses 3 typical cases in arid area of Mongolia, representing the convection and advection precipitation process, the 3 cases are simulated and analyzed by using WRF and FLEXPART model. The results show that the precipitation and recycling process in arid area of Mongolia, noon local evaporation exceeds precipitation, land surface water vapor by means of evaporation into the atmosphere, local water vapor contribution reaches the maximum (0.1mm), recycling process began to increase, reached the maximum in the evening (10%), precipitation recycling could strengthen the effect of reducing water and precipitation in turn At the same time, the rate reached the maximum (7%), precipitation, evaporation also reaches the maximum. Then the local moisture contribution gradually decreased, reached the lowest in the morning to morning all day long evaporation, local water vapor contribution is negative (ET-P-0.2 mm). This feature in the advective precipitation process is more obvious. In addition, through the analysis on the change the characteristics of rainfall variables such as the case. Results show that the precipitation, evaporation in arid area of Mongolia, precipitation transformation and precipitation recycling rate variation periods of quasi 10 day, which is similar to the average precipitation and climate. In daily scale recycling for the precipitation change has negative feedback mechanism: when the precipitation decreases after evaporation add more water vapor from the ground, into the atmosphere through evaporation, precipitation in recycling, compensation precipitation. In spatial distribution, arid area Mongolia precipitation recycling uneven distribution in lakes, runoff and ground Humidity areas, due to strong evaporation, precipitation recycling rate is strong. In the precipitation process, the main contribution to the external water vapor zonal moisture transport, the total precipitable water in about 40%. While the meridional water vapor transport accounted for 7%~20%, and the meridional moisture transport is strong, large rainfall, global warming and vice versa. Have an important impact on the water cycle. This paper analyzes the different emission scenarios of water cycle variations. The results show that the Atmospheric Precipitable Water in the future in different stages of heating showed a growth trend and distribution in different degree, which is determined by the temperature increase of atmospheric water holding capacity and ET-P are due. Arid area increased, humid area decreased, showing the trend of dry arid, humid area and arid area is wet, precipitation conversion rate and precipitation recycling rate was decreased, with global temperature show Rise, arid area local water circulation weakened. In different periods the next twenty-first Century, the global land average precipitation conversion rate and recycling rate showed a weakening trend, reduced by 1.5% and 0.7% respectively, the RCP8.5 scenario decreased more significantly, the negative anomaly of -2.7% and -0.9%. in the typical arid region, precipitation will be temperature increases, increased up to 1.85 mm day-1 10a-1. although the atmospheric water vapor content increased significantly, but the conversion of arid region water vapor rate decreased, indicated that the global temperature rise makes the water holding capacity of the atmosphere increases. And the overall performance of arid area net water output, reduced precipitation recirculation rate showed that the local evapotranspiration due to the flat current output, did not participate in the local precipitation recycling. Total precipitation, water vapor transport from external advection is enhanced and accelerated, the said global warming, atmospheric water circulation speed But there is no significant change in ET-P, which indicates that the acceleration of large scale water cycle does not make significant dry and wet changes in the arid regions of China and Mongolia.

【学位授予单位】：兰州大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P467;P339

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